Commonly used masks in a photo of a liquid crystal display comprise a full tone mask (FTM) containing only 0 and 100% transmittance, and a gray tone mask (GTM), which utilizes a line pattern of a periodic arrangement of high-precision and small critical dimension (CD) to uniformly reduce the transmittance of an area, and there are also half tone masks (HTMs) forming a desired transmittance between 0 and 100%, that are formed through a special process to create a semipermeable membrane in a specific area. BPS 1Tone technology patterns an organic photosensitive resin containing a black dye by using FTM, and a single pass forms a photoresist spacer (PS) and a black matrix (BM). Because of a great thickness of a film coating, in an absence of an intermediate transmittance region, a height of a light shielding area of the BM is too large, which is a manufacturing risk point.
For a situation of a continuous overlapped color resist CF or an organic film PFA leveling, a BM barrier is easily formed when coating a thick BPS film because the FTM has no semi-transmissive area and only a difference between a film formation and a non-film formation. Therefore, it is possible to dredge the color resist development into an isolated island pattern, and use a terrain pit to reduce an overall height of the BPS in the area. However, to ditch the color-resisting area such as the data line, it is still necessary to cover the BM to shield the light, in this case, the width CD of the BM needs to be controlled: too narrow will result in a light leakage, and too wide will result in an overlapping horn bulge, which makes a local area more rugged; but in order to avoid the light leakage and offset a deviation of a machine, generally a larger width of a design is chosen, so a horn bulge is difficult to avoid, in serious situation, it will produce the risk.
There are other methods to have a composite film of different photosensitive properties, formed by an exposure of an image with a small inclination to further reduce the height of the BM, but a controllability of the process is low, and time and cost is high.